1. Field of the Invention
The present invention relates to a liquid crystal display apparatus and a method for grounding the liquid crystal display apparatus.
2. Description of the Related Art
Generally, a liquid crystal display apparatus includes a liquid crystal display panel, a backlight unit and a chassis (case). The backlight unit is arranged at a back face of the liquid crystal display panel. The liquid crystal display apparatus includes a structure in which the liquid crystal display panel integrated with the backlight unit is installed in a metallic frame (i.e. the chassis).
The liquid crystal display panel includes a liquid crystal driving circuit substrate, an opposite substrate, a sealing member and a liquid crystal material. The liquid crystal driving circuit substrate and the opposite substrate are oppositely arranged with a gap therebetween which is formed by the sealing member. The liquid crystal material is disposed in the gap to form the liquid crystal display panel. The liquid crystal driving circuit substrate includes a liquid crystal driving circuit on a surface thereof (the inner surface) which contacts the liquid crystal material.
Some opposite substrates of the liquid crystal display panels do not include a conductor on surfaces thereof. That is, such opposite substrate is not connected electrically anywhere and consequently, is in an electrically floating state. For example, a liquid crystal display apparatus of a normally black mode type according to IPS (In-Plane Switching) method includes the opposite substrate above mentioned.
A polarizing plate including a conductor on a surface thereof thereon is attached to a surface of the opposite substrate in the electrically floating state in order to discharge an electric charge (i.e. static electricity) on the opposite substrate. The opposite substrate is grounded (GND) when the conductor mounted on the surface of the polarizing plate contacts the metallic frame.
In such liquid crystal display panel, the polarizing plate at the opposite substrate side is smaller than an external shape of the liquid crystal display panel. Therefore, the conductor for grounding is pressed physically by the metallic frame against the polarizing plate arranged on a surface of the liquid crystal display panel. As a result, a stress is applied to the liquid crystal display panel, and consequently, the stress causes an uneven image on a screen.
Methods for grounding from the surface of the polarizing plate at the opposite substrate side according to a related art will be described in FIG. 3 to FIG. 7. Japanese Patent Application Laid-Open No. 2004-355035 (Japanese Patent Application No. 2004-270865) discloses a liquid crystal display apparatus having a structure for grounding the opposite substrate mentioned above. FIG. 3 is a cross sectional view showing the disclosed liquid crystal display apparatus. FIG. 4 is a cross sectional view showing a structure of the polarizing plate shown in FIG. 3. FIG. 5 is a fragmentary cross sectional view showing details of the liquid crystal display panel shown in FIG. 3.
The liquid crystal display apparatus shown in FIG. 3 includes a liquid crystal material 11, an upper polarizing plate 13b, a conductor 16a, a metallic frame 180, a lower polarizing plate 15a, a backlight unit 19 and a printed wiring board 21. The conductor 16a includes, for example, a conductive rubber and forms electrical connection between the upper polarizing plate 13b and the metallic frame 180.
As shown in FIG. 4, the upper polarizing plate 13b includes a three-layered structure having an optical polarizing layer 131, a conductive layer 132 and an antireflection layer 133. Both-sided adhesive tapes formed on both sides of the conductor 16a bond the upper polarizing plate 13b and the conductor 16a and bond the metallic frame 180 and the conductor 16a. The conductive layer 132 is, for example, an ITO (Indium Tin Oxide) film formed with the sputtering method. A film made of SiO2 is formed as the antireflection layer 133 on the surface of the conductive layer 132 for protection thereof.
An opposite substrate 12 and an opposite substrate side polarizing plate 13a shown in FIG. 5 correspond to the upper polarizing plate 13b shown in FIG. 3. A liquid crystal driving circuit substrate 14 and a liquid crystal driving circuit side polarizing plate 15b shown in FIG. 5 correspond to the lower polarizing plate 15a shown in FIG. 3. The liquid crystal display panel has a structure that the liquid crystal driving circuit substrate 14 and the opposite substrate 12 are oppositely arranged with a predetermined gap and are sealed by a sealing member 17. The liquid crystal material 11 is disposed in the gap therebetween. The polarizing plate 13a at the opposite substrate side is adhered to a front surface (i.e. a display surface side) of the liquid crystal display panel. The polarizing plate 15a at the liquid crystal driving circuit side is adhered to a rear surface of the liquid crystal display panel.
According to the structure shown in FIG. 5, when the metallic frame 180 presses the conductor 16a against the polarizing plate 13a at the opposite substrate side arranged on the surface of the liquid crystal display panel, an electrical grounding is secured. However, stress is applied to the liquid crystal display panel, and consequently, an uneven image on a screen due to the stress is generated. If the stress is made so small that the uneven images do not occur, the electric resistance between the polarizing plate 13a at the surface of the opposite substrate side and the metallic frame 180 via the conductor 16a becomes large. As a result, the electric charge can not be discharged sufficiently.
FIG. 6 is a fragmentary cross sectional view showing other liquid crystal display apparatus disclosed in Japanese Patent Application Laid-Open No. 2004-355035. According to the disclosed structure, the metallic frame 180 and the polarizing plate 13a at the opposite substrate side are connected electrically each other through a conductive tape 20, instead of the conductor 16a. In this case, since the conductive tape 20 is adhered to the surface of the polarizing plate 13a at the opposite substrate side, the electric charge can be discharged to the metallic frame 180 without the stress originated with the metallic frame 180 which is applied to the surface of the liquid crystal display panel. However, according to the structure, when the liquid crystal display panel and the backlight unit 19 are installed in the metallic frame 180, it becomes necessary to perform a step for adhering the conductive tape 20 which is an extra process. As a result, production cost of the liquid crystal display apparatus increases due to the additive step in the assembly process of the apparatus.
FIG. 7 is a fragmentary cross sectional view showing further other liquid crystal display apparatus disclosed in Japanese Patent Application Laid-Open No. 2004-355035. According to the apparatus, a conductive tape 20a is used. Here, the conductive tape 20a is adhered to a metal part 22 of the backlight unit 19 instead of the metallic frame 180. Accordingly, the apparatus includes the same difficulty as the apparatus shown in FIG. 6.